Jayne Rowse, left, and her partner April DeBoer are asking a judge to overturn a Michigan law that bans same-sex marriage. . / Bill Pugliano/Getty Images

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Associated Press

A California scholar is the next witness in the trial over the future of Michiganís ban on gay marriage.

Gary Gates of the Williams Institute at UCLA law school co-authored a book on demographics of the gay and lesbian population. Heís used census data to study the characteristics of same-sex couples.

Gates is expected to testify Thursday in federal court in Detroit. Detroit-area nurses Jayne Rowse and April DeBoer are asking a judge to overturn a Michigan law that bans same-sex marriage. They say it violates their rights under the U.S. Constitution.